slow execution of built executables on a Mac

Carter Schonwald carter.schonwald at
Fri Oct 26 21:02:53 UTC 2018

theory one:

are you setting the intree gmp flag? and/or  dont have gmp the library
installed? maybe your ghc is using integer simple!

theory two: dont set -j greater than about 8 or perhaps 16? (some parts of
ghc are slower on too paralle a setup?)

those are my two off the cuff guesses

you could also look at system monitor to see if your'e being IO bound or
memory or CPU bound
(possible failure siutation: the repo is under dropbox or something and
dropbox is eating your memory bandwidth trying to sync stuff?)

On Fri, Oct 26, 2018 at 2:33 PM Richard Eisenberg <rae at>

> Hi devs,
> I have a shiny, new iMac in my office. It's thus frustrating that it takes
> my iMac longer to build GHC than my trusty 28-month-old laptop. Building
> devel2 on a fresh checkout takes just about an hour. By contrast, my laptop
> is done after 30 minutes of work (same build settings). The laptop has a
> 2.8GHz Intel i7 running macOS 10.13.5; the desktop has a 3.5GHz Intel i5
> running macOS 10.13.6. Both bootstrapped from the binary distro of GHC
> 8.6.1.
> Watching GHC build, everything is snappy enough during the stage-1 build.
> But then, as soon as we start using GHC-produced executables, things slow
> down. It's most noticeable in the rts_dist_HC phase, which crawls. Stage 2
> is pretty slow, too.
> So: is there anything anyone knows about recent Macs not liking locally
> built executables? Or is there some local setting that I need to update?
> The prepackaged GHC seems to work well, so that gives me hope that someone
> knows what setting to tweak.
> Thanks!
> Richard
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